The present invention generally relates to thermoplastic silicone-containing materials useful as a hydrogel contact lens material.
Hydrogels represent a desirable class of materials for many biomedical applications including contact lenses. Hydrogels are hydrated, cross-linked polymeric system that contain water in an equilibrium state. Silicone hydrogels are a known class of hydrogels and are characterized by the inclusion of a silicone-containing material. Typically, a silicone-containing monomer is copolymerized by free radical polymerization with a hydrophilic monomer, with either the silicone-containing monomer or the hydrophilic monomer functioning as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed. Such silicone hydrogels, based on polyurethanes, are disclosed in U.S. Pat. No. 5,034,461, for example. An advantage of silicone hydrogels over non-silicone hydrogels is that the silicone hydrogels typically have higher oxygen permeability due to the inclusion of the silicone-containing monomer. Because such hydrogels are based on monomers polymerizable by free radical, these materials are thermosetting polymers.
The present invention provides a class of silicone hydrogel materials that are thermoplastic. These materials can be cast into articles such as contact lenses by methods other than free radical polymerization, for example, by compression molding or injection molding. The materials include a silicone-containing moiety and a highly hydrophilic moiety, thus the materials exhibit relatively high oxygen permeability while being able to absorb and retain water. When cast into contact lenses, the materials are optically clear, and the materials are stable at relatively high temperatures.